The incidence of delirium in the ICU has been described as 50%. In mechanically ventilated patients the incidence increases to 80%. Delirium is considered an independent factor of bad prognosis. It increases the days under mechanical ventilation, hospital length of stay, the dependence at discharge and the risk of death. Because of that, it has a high impact in health and in economic cost. However it is an underdiagnosed illness due to the absence of ICU protocols for the correct diagnosis. The scale Confusion Assessment Method for ICU (CAM - ICU) is the validated tool for the screening and it is used by the nurses and physicians.